Catalyst deterioration determination system

Abstract

A catalyst deterioration determination system effectively prevents erroneous determination caused by increase of the H2 component in exhaust gas and improves accuracy of determination. A LAF sensor and an O2 sensor are provided on the upstream side and downstream side of a three-way catalyst. Deterioration of the three-way catalyst is determined on the basis of an output of the O2 sensor, which is detected during air-fuel ratio switching control in which an air-fuel ratio is alternately switched to the rich side and lean side of the stoichiometric air-fuel ratio according to a detected equivalent ratio detected by the LAF sensor, on the basis of a result of comparison between an oxygen inflow into the three-way catalyst and a lean side-limiting value and a rich side-limiting value which are target values of the oxygen inflow. Fuel injection timing retardation control and/or divided fuel injection control are prohibited during the deterioration determination.

The invention claimed is: 
     
       1. A catalyst deterioration determination system configured to determine deterioration of a catalyst, the catalyst being provided in an exhaust system of an internal combustion engine, having an oxygen storing capacity, and purifying exhaust gas, the system comprising:
 a first oxygen concentration sensor that is provided on the upstream side of said catalyst; 
 a second oxygen concentration sensor that is provided on the downstream side of said catalyst; 
 an oxygen inflow calculation controller configured to calculate an amount of oxygen flowing into said catalyst as an oxygen inflow; 
 air-fuel ratio switching controller configured to perform air-fuel ratio switching control in which control is performed to alternately switch an air-fuel ratio of an air-fuel mixture supplied to said internal combustion engine between a rich side and a lean side of a stoichiometric air-fuel ratio, according to an oxygen concentration detected by said first oxygen concentration sensor, on the basis of a result of comparison between said calculated oxygen inflow and a target value of the oxygen inflow; 
 a deterioration determination controller configured to perform a deterioration determination by determining deterioration of said catalyst, on the basis of an output of said second oxygen concentration sensor detected during the air-fuel ratio switching control; and 
 a prohibition controller configured to prohibit, during the deterioration determination by the deterioration determination controller, both or any one of retard control in which a fuel injection timing is retarded, and divided injection control in which fuel is injected in multiple divided times. 
 
     
     
       2. The catalyst deterioration determination system according to  claim 1 , further comprising a fuel injection mode controller configured to determine a fuel injection mode in accordance with a temperature of the engine,
 wherein the fuel injection mode controller performs both or any one of the retard control and the divided injection control when the temperature of the engine is lower than a predetermined value which indicates the engine is in a cold state, and performs a normal injection control when the temperature of the engine is equal to or higher than the predetermined value, 
 wherein the prohibition controller determines whether the deterioration determination is being performed by the deterioration determination controller, and if so, prohibits both or any one of the retard control and the divided injection control even though the temperature of the engine is lower than the predetermined value. 
 
     
     
       3. A catalyst deterioration determination method determining deterioration of a catalyst, the catalyst being provided in an exhaust system of an internal combustion engine, having an oxygen storing capacity, and purifying exhaust gas, the method comprising steps of:
 calculating, by using a controller, an amount of oxygen flowing into said catalyst as an oxygen inflow; 
 performing, by using the controller, air-fuel ratio switching control in which control is performed to alternately switch an air-fuel ratio of an air-fuel mixture supplied to said internal combustion engine between a rich side and a lean side of a stoichiometric air-fuel ratio, according to an oxygen concentration detected by a first oxygen concentration sensor, on the basis of a result of comparison between said calculated oxygen inflow and a target value of the oxygen inflow, wherein the first oxygen concentration sensor is provided on the upstream side of said catalyst; 
 performing, by using the controller, a deterioration determination by determining deterioration of said catalyst, on the basis of an output of a second oxygen concentration sensor detected during the air-fuel ratio switching control, wherein the second oxygen concentration sensor is provided on the downstream side of said catalyst; 
 prohibiting, by using the controller, during performing the deterioration determination, both or any one of retard control in which a fuel injection timing is retarded, and divided injection control in which fuel is injected in multiple divided times. 
 
     
     
       4. The catalyst deterioration determination method according to  claim 3 , further comprising:
 determining, by using the controller, a fuel injection mode in accordance with a temperature of the engine so as to perform both or any one of the retard control and the divided injection control when the temperature of the engine is lower than a predetermined value which indicates the engine is in a cold state, and perform a normal injection control when the temperature of the engine is equal to or higher than the predetermined value, 
 wherein the step of prohibiting determines whether the deterioration determination is being performed, and if so, prohibits both or any one of the retard control and the divided injection control even though the temperature of the engine is lower than the predetermined value.